The present invention relates to a hydraulic drive for a press, in particular for a sheet metal forming press, said press comprising a press ram adapted to be moved up and down, and a hydraulically displaceable counter support, said counter support being adapted to be moved in a forward stroke in the direction towards the press ram via a hydraulic cylinder by means of a first hydrostatic machine, and said counter support being adapted to be moved by said press ram in a return or rearward stroke.
For example, DE-AS 20 43 967 discloses a sheet metal forming press having a press ram and a counter support and a hydraulic drive with the features mentioned above. In said known press a pump pumps oil into the hydraulic cylinder during the forward stroke of the counter support. As soon as the counter support has reached its end position, the supply of pressure medium from the pump driven by an electric motor to the cylinder is interrupted by means of control valves. When the counter support is displaced during the return stroke by means of the press ram, a certain pressure has to be maintained in the cylinder. It is generally known that for this purpose the pressure medium is drained into the pressure medium container or tank by means of a relief (or pressure limiting) valve, a flow control (or throttle) valve or a proportional valve. See for instance, EP 0 173 755 B1. When draining the pressure medium via the relief valve or via the flow control valve a large amount of heat is generated which gets lost without being used. Possibly even cooling has to be provided. This means additional cost for structural components.